Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/18503#discussion_r128439416
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/HDFSBackedStateStoreProvider.scala
---
@@ -363,7 +363,8 @@ private[state] class HDFSBackedStateStoreProvider
extends StateStoreProvider wit
val valueRowBuffer = new Array[Byte](valueSize)
ByteStreams.readFully(input, valueRowBuffer, 0, valueSize)
val valueRow = new UnsafeRow(valueSchema.fields.length)
- valueRow.pointTo(valueRowBuffer, valueSize)
+ // If valueSize in existing file is not multiple of 8, round
it down to multiple of 8
+ valueRow.pointTo(valueRowBuffer, (valueSize / 8) * 8)
--- End diff --
yes, because the extra bytes that exceed the 8-bytes boundary in
`UnsafeRow` will never be read, so it's safe to ignore them. And here we still
respect the row length when reading the binary, so no data will be missed.
@kiszk can we add more comments to explain why this can happen? We should
say that before Spark 2.3 we mistakenly append 4 bytes to the value row in
aggregate buffer, which gets persisted into the checkpoint data and so on
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